The long term goal of this research is to define the mechanisms by which photoperiod, hormones of the hypothalamus, pituitary and ovary interact in controlling cessation and reinitiation of embryonic development and implantation in a species exhibiting obligate delay of implantation. This proposal specifically seeks to Provide additional evidence to support the theory that corpora lutea of mustelid carnivores such as the domesticated ferret and spotted skunk secrete a proteinacious compound that is essential for induction of blastocyst implantation. I propose to further purify and chemically characterize the ferret luteal implantation factor (LIF) and to determine which trophic factor(s) stimulate its synthesis and secretion in vitro. I then propose to demonstrate by passive immunization of ferrets and spotted skunks, that antibodies to LIF will inhibit implantation. Another experiment is designed to determine on which days of pregnancy or pseudopregnancy LIF is secreted in ferrets. I also propose to further verify that LIF is only produced by CL of ferrets and to explore its subcellular distribution and mode of secretion using immunocytochemistry. Another series of experiments is designed to determine whether LIF acts on the uterus and or blastocysts and to provide evidence for the presence of receptor sites to this compound. This will be accomplished by studying specific binding of (125I)-LIF to uterine and blastocyst plasma membranes. Further demonstration of specific receptor sites will be accomplished by extraction of cross-linked (125I)-LIF-receptor complexes, followed by electrophoresis and autoradiography. The last set of experiments is designed to determine the specific effects of LIF on its target organs by measuring such things as changes in cAMP, protein, RNA and DNA synthesis in the uterus and or blastocysts.